query in partial classes

Question

Hello, good afternoon everyone, I have a problem making a list with linq with join, I have the following classes

namespace CapaDatos
{
    using System;
    using System.Collections.Generic;

    public partial class tblCategoria
    {
        [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Usage", "CA2214:DoNotCallOverridableMethodsInConstructors")]
        public tblCategoria()
        {
            this.tblProductos = new HashSet<tblProducto>();
            this.tblDetalleVentas = new HashSet<tblDetalleVenta>();
        }

        public int Id { get; set; }
        public string Descripcion { get; set; }
        public byte[] Fotografia { get; set; }
        public Nullable<int> Estado_Id { get; set; }

        public virtual tblEstado tblEstado { get; set; }
        [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Usage", "CA2227:CollectionPropertiesShouldBeReadOnly")]
        public virtual ICollection<tblProducto> tblProductos { get; set; }
        [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Usage", "CA2227:CollectionPropertiesShouldBeReadOnly")]
        public virtual ICollection<tblDetalleVenta> tblDetalleVentas { get; set; }
    }
}

As you will see, it is a partial class

therefore to create my methods create another class with the same name, but with a different file name, since I cannot create it with the same name

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace CapaDatos
{
    public partial class tblCategoria
    {
        string NombreEstado;
        public static void GuardarCategoria(tblCategoria tblCategoria)
        {
            using (GourmetEntities db = new GourmetEntities())
            {
                db.tblCategorias.Add(tblCategoria);
                db.SaveChanges();
            }
        }
        public static List<tblCategoria> ListaCategorias()
        {
            using (GourmetEntities db = new GourmetEntities())
            {
                var Lista = (from List in db.tblCategorias
                             join e in db.tblEstados on List.Estado_Id equals e.Id
                             select new tblCategoria
                             {
                                    Descripcion = List.Descripcion,
                                    NombreEstado = e.NombreEstado, // this field comes from the tblStates table
                             }).ToList();

                return Lista;
                //return db.tblCategorias.ToList(); ok
            }
        }
    }
}

 The "StateName" field is not in the table or in the model

 When I run the program and try to load into a datagridview it shows me the following

 

System.NotSupportedException: 'The entity or complex type 'GourmetModel.tblCategoria' cannot be constructed in a LINQ to Entities query.'

 

Esta excepción se generó originalmente en esta pila de llamadas:

[Código externo]

CapaDatos.tblCategoria.ListaCategorias() en OperacionCategorias.cs

CapaPresentacion.Frm_VisorImagenes.CargarDataGridCategorias() en Frm_VisorImagenes.cs

CapaPresentacion.Frm_VisorImagenes.Frm_VisorImagenes_Load(object, System.EventArgs) en Frm_VisorImagenes.cs

[Código externo]

I have both classes in the same layer and both are partial, please help me solve this problem, thank you all very much.

Ro